The invention relates to a suspension of a vehicle wheel on a vehicle body, including a spring element accommodating the compressive forces acting between a vehicle and the vehicle body and a linear actuator for adjusting the vehicle height.
A vehicle wheel is coupled to the vehicle body via such a wheel suspension, which provides for damped spring support of the vehicle body on the vehicle wheel. It also determines the kinematics of the vehicle wheel and the axis of rotation of the vehicle wheel. The wheel kinematics or axle kinematics comprise, in particular, the toe-in and the camber of the wheel. Moreover, such a wheel suspension may have integrated into it a level control, with the aid of which the (vertical) distance between the vehicle wheel and the vehicle body can be set.
A suspension of this type generally comprises a spring strut or it is in the form of a spring strut. Such a spring strut contains a spring element. Moreover, a damping element or a damper unit may be integrated into a spring strut. Furthermore, it is possible to integrate a level-control actuator into a spring strut.
Whilst, in a passive suspension, the spring characteristic curve of the wheel suspension is constant, in an active suspension the spring characteristic curve is adapted dynamically to the respective driving situation. With an active suspension, the driving behavior of the vehicle can be influenced positively and vehicle safety increased. Furthermore, it is possible to vary the kinematics, in particular the distance between the vehicle and vehicle suspension, dynamically as a function of the respective driving situation, in order also thereby to improve the drive-dynamic properties of the vehicle. A vehicle chassis which is equipped with an adjustable suspension of this type and/or with such adjustable kinematics is also designated as an xe2x80x9cactive chassisxe2x80x9d.
DE 195 47 535 C2 discloses a self-pumping hydropneumatic spring strut with internal level control, which has a working cylinder and a piston pump. The working cylinder carries on a piston rod a piston, which subdivides the working cylinder into two working spaces. The working cylinder is surrounded co-axially by a low-pressure chamber and a high-pressure chamber. Gas and a liquid damping medium are accommodated in the low-pressure chamber, whilst the high-pressure chamber separates the liquid damping medium from the gas volume by means of a diaphragm. A pump rod is held via a holding element between the upper working space of the working cylinder and the high-pressure chamber, the holding element at the same time fixing a valve. The piston rod of the working cylinder is hollow and has a cavity forming a pump cylinder, into which the pump rod extends.
DE 201 07 329 U1 discloses a positioning device operating with a plurality of linear actuators which are formed in each case from a tubular contraction element. A contraction element of this type possesses a fluidic pressure chamber encased by a casing. The casing is designed in such a way that a pressure rise in the pressure chamber widens the casing radially and shortens it axially. The casing consists, for example, of a leak-tight flexible tube, around which high-tensile fibers are spun in a diamond-shaped manner. The three-dimensional lattice structure formed in this way is deformed in a circumferential direction when the pressure rises in the pressure chamber. At the same time, a desired tensile force occurs in the axial direction.
DE 690 14 488 T2 discloses a further wheel suspension having a spring element, a damping element and an electromechanical linear actuator, which is expediently designed as an electric linear motor.
It is the object of the present invention to provide a particularly advantageous embodiment for a wheel suspension of the type mentioned in the introduction.
In a suspension of a vehicle wheel on a vehicle body, including a spring element for accommodating the compressive forces acting between the vehicle wheel and the vehicle body and with a linear actuator for adjusting the kinematics and the distance between the vehicle wheel and vehicle body, the spring element and the linear actuator include at least one tubular contraction element with at least one hydraulic or pneumatic or hydropneumatic pressure chamber enclosed in a casing, which is designed in such a way that a pressure rise in the pressure chamber widens the casing radially and shortens it axially.
The invention is based on the general idea of forming a spring element and/or a linear actuator of the wheel suspension by means of a tubular contraction element of the above-mentioned type. A particular advantage of this form of use is seen in the low weight of the tubular contraction element, with the result that considerable weight saving can be achieved on the vehicle. Furthermore, relatively high dynamics, along with comparatively high actuating forces, can be achieved by means of relatively low pressures and low volume flows. In particular, it is thereby possible to implement active springing by means of a gaseous medium.
According to a particular advantageous embodiment of the invention, a force deflection device is provided, which converts the compressive forces occurring between the vehicle wheel and vehicle body into tensile forces. The contraction element is supported on the vehicle wheel and on the vehicle body via the force deflection device. With the aid of a force deflection device of this type, it is possible to use a linear actuator, which per se can generate only tensile forces, or a spring element, which per se possesses the desired springing property in the tension direction only, in a wheel suspension in which the vehicle wheel is supported on the vehicle body by a spring structure which is subjected to compressive forces.
With the aid of this force deflection device, therefore, it is possible to use the contraction element as a tension-spring element or as a tensile linear actuator in the wheel suspension.
A force deflection device of this type may have a lever arrangement which is supported, on the one hand, on the vehicle wheel and, on the other hand, on the vehicle body, the contraction element being connected, at one end, to the vehicle body and, at the other end, to the lever arrangement, in particular via a rocker lever supported on the vehicle body. By means of this lever arrangement, the available tensile forces can be deflected relatively simply to accommodate the compressive forces, and, moreover, it is possible for the contraction element used in each case to provide on the vehicle body a suitable arrangement which depends, for example, on the available installation space. For example, the contraction element may be arranged vertically or horizontally, in the vehicle longitudinal direction or transversely to the latter.
In a particular embodiment, the force deflection device may have two support elements designed to be displaceable one in the other in the spring-compression direction of the vehicle wheel with respect to the vehicle body. One support element is secured with its fixed end to the vehicle wheel, whilst the other suppor element is secured with its fixed end to the vehicle body. The contraction element is arranged coaxially to the support elements and is connected, at one end, to the free end of one support element and, at the other end, to the free end of the other support element. With the aid of the force deflection device provided in this way, the same installation position which, for example, a conventional helical compression spring has in a conventional spring strut is achieved with the contraction element which per se can absorb or generate only tensile forces. By means of the support elements, direct force transmission takes place between the vehicle wheel and vehicle body, on the one hand, and the contraction element, on the other hand. However, the effective direction of the forces is reversed. By virtue of this arrangement, the performance capability of the contraction element can be utilized optimally.
The contraction element supported axially between the free ends of the support elements may be used, for example, as a spring element. In a particularly simple embodiment, the pressure chamber of the contraction element may be filled with a gaseous fluid. In this case, spring characteristic curves similar to those of a helical steel compression spring can be generated. By the pressure chamber being connected to a pressure control device, the characteristic curve of the spring suspension thus formed can be varied, in particular adapted dynamically. Furthermore, a level control is provided as a result. If a hydraulic fluid is used, a spring accumulator for volume compensation is necessary in the hydraulic circuit.
In one embodiment, one of the two support elements may have a helical compression spring, via which the ends of this support element are supported on one another. In this embodiment, functional separation may be carried out in such a way that the contraction element is operated solely as a linear actuator, whilst the helical compression spring provides essentially only the spring action. Combinations are also possible in which both, the helical compression spring and the contraction element, exert a spring action.
According to a particular embodiment, the contraction element may be of annular design and have an outer casing and an inner casing arranged concentrically to the latter, the outer casing encasing the pressure chamber radially on the outside and the inner casing encasing the pressure chamber radially on the inside. The two casings are designed in such a way that a pressure rise in the pressure chamber shortens both casings axially and widens the outer casing radially outwards and the inner casing radially inwards. In this embodiment, the pressure chamber is thus designed as a toroidal annular chamber. Relatively high tensile forces, along with relatively small volume changes in the pressure chamber, can thereby be implemented.
In one embodiment, this annular contraction element may contain centrally an axial passage which is surrounded by the inner casing. In this embodiment, a damper unit may extend co-axially through this passage and be connected, at one end, to the vehicle wheel, and at the other end, to the vehicle body. A particularly compact design is thus obtained.
In another embodiment, the central axial passage enclosed by the inner casing is in communication with the pressure chamber of the contraction element. In particular, a flow-damping member may then be arranged between the pressure chamber of the annular contraction element and the inner passage. Furthermore, it is possible to connect the pressure chamber of the annular contraction element indirectly via the inner passage to a pressure source or to a pressure generator. These measures simplify the set-up of the arrangement as a whole. In this embodiment, a gas volume may be arranged in the passage or in the pressure chamber of the contraction element, said gas volume permitting volume compensation.
In a particular embodiment, a further contraction element may be arranged co-axially in the passage. Then the pressure chamber of the inner contraction element is filled with a gas, whilst the passage and the pressure chamber of the outer contraction element are filled with a hydraulic fluid. In this design, the inner contraction element forms a gas accumulator which is sealed off hermetically with respect to the hydraulic medium surrounding it.
In another embodiment, at least one inner contraction element may be arranged in the pressure chamber of an outer contraction element, the pressure chamber of the inner contraction element being filled with a hydraulic fluid, whilst the pressure chamber of the outer contraction element is filled with gas or with gas and hydraulic fluid. In this embodiment, the at least one inner contraction element serves solely as a tensile linear actuator, while the outer contraction element serves for volume compensation, as passive spring suspension and, in particular, also can be used for level control. In this embodiment, the volume flows necessary for achieving an axial adjusting movement of the inner contraction element are relatively low, so that the linear actuator thus produced can be operated with high dynamics.
As far as the contraction element used as tension-spring element is operated with a hydraulic medium, a spring accumulator must be in communication with the pressure chamber for volume compensation. A spring accumulator of this type, in ah advantageous embodiment, contains at least one contraction element of the above-described type, the pressure chamber of this contraction element being filled with a hydraulic fluid and being connectable via a corresponding connection to a hydraulic circuit, in which the spring accumulator ensures the necessary volume compensation. The contraction element engages, at one end, a base and, at the other end, a spring plate. Arranged co-axially to the contraction element is a helical compression spring, which is supported, at one end, on the base and, at the other end, on the spring plate. With the aid of this helical compression spring, a spring force counteracting the contraction of the contraction element can be introduced to the contraction element. A pressure increase in the pressure chamber leads to a shortening in length of the casing. This movement is counteracted by the helical compression spring, with the result that the desired spring action of the spring accumulator is established.
Important features and advantages of the invention will become apparent from the following description of the invention with reference to the accompanying drawings.
Exemplary embodiments of the invention are illustrated in the drawings and explained in greater detail in the following description.